Manufacture of compressed tablets and the like from finely divided ingredients



CREEVY MANUFACTURE OF COMPRESSED TABLETS AND THE June 29, 1948. c.

LIKE mom FINELY nrvnmn INGREDIENTS Filed July 16,-1945 Attorney Patented June 29, 1948 OFFICE MANUFACTURE OF COMPRESSED TABLETS AND THE LIKE FROM FINELY DIVIDED INGREDIENTS Charles Creevy, Greenforiingland, as'slgn'or to Glaxo Laboratories Limited, Greenford, England, a company of Great Britain Application July 16, 1945, Serial No. 605,336 In Great Britain May 11, 1944 Section 1, Public Law 690, August 8, 1946 Patent expires May 11, 1'96! 1-4 Claims. (01. 107-48) This invention is concerned with improvements in and relating to the manufacture of compressed tablets-and the like from finely divided ingredients, and it relates more particularly to the provision of an improved tableting machine.

It is often desired to prepare finely divided materials in the form of compressed tablets, and the usual method is to feed the material into a die or mould and compress it between movable rams or punches, one of which is adapted to expel the compressed tablet from the die, and then to be moved from the tablet-expelling position into that for the reception of the next charge of material.

Considerable difiiculty is however often experienced in removing the compressed article from the die or mould, owing to the adhesion of the material to the sides of the die, and many attempts have been made to overcome this dimculty. Thus, in many cases materials such for example as powdered stearine or talc have been added to the charge to facilitate ejection of the tablet. Another method which has often been used is to spray or mix solutions of oils, waxes or fats into the material Both these methods, however, have obvious disadvantages, as in many cases it is undesirable that the tablet should contain substances such as these stated additions. Thisapplies particularly to the compression of drugs orchemlcals which are subsequently to be used in solution. Moreover the use of these added substances, which are intended to act as lubricants to the whole of the charge to becompressed is necessarily wasteful, as only that part of the lubricant which is in contact with the walls of the die when the tablet has been compressed serves the intended purpose of facilitating its ejection.

In further efforts to overcome this difliculty it was found that a compressed tablet of a material difiicult to eject from the die, such for -example as sodium calcium lactate, though compressed from material to which no lubricant had been added could be easily removed from the die if its inner walls had first been smeared with a faint trace of an edible oil or wax in solution, and this observation led to attempts to overcome the difficulty by providing means for regularly supplying lubricant to the walls of the die. The usual method has been to cut a slot or groove into the lower punch or ram, and fit an absorbent washer into the groove, this washer being soaked in a lubricant; as the punch moves upwards to eject a tablet the washer thus supplies a smear-of lubricant ready for the next operation.

. 2 This idea has been further developed by drill: ing through the punch and the punch-holding device, and thus connecting the washer to a pump by means of which lubricant is always made available.

. The disadvantage of the former method is that the machine has frequently to be stopped in order to supply fresh lubricant to the washer whllst ln the latter case it was often found that fine particles of the material to be compressed tended to move downwards between the punch and the die and to seal the lubricating washer.

Theobject of the present invention is to overcome these difliculties and to provide improved means for the manufacture of compressed tablets and the like. 4 I

It has been found that by constructing the wall of the compression chamber in a tableting ma chine of a suitable porous metal and supplying a liquid lubricant. under pressure to said porous metal a film of lubricant can readily be formed on the inner wall; of the compression chamber, thus enabling materials which normally tend to bind in the die and to beejectable therefrom only with diiliculty to be easily tableted without the need of adding lubricants to them. 4

Accordingly the invention comprises a tableting machine in which. the material to be tableted is compressed within a die of porous metal housed within a non-porous housing, the machine having means for causing a liquid lubricant to be exuded through the pores of said porous metal so as to create a lubricating film over the face of the die.

In order to prevent lubricant from exuding through the end face of thedie and thereby tending to foul the ingoing material to be compressed, it is desirable that the walls of the compression chamber or die should not be porous at the upper or inlet end, and for this purpose the die may either :be constructed of a size slightly shorter than the depth of the chamber and mounted so asto have a short nonporous part of the diehousing at the inlet end, or the die may be constructed so that it is non por-ous over a short portion of its lengths at one end, and it maybe mounted so that this portion acts as a seal to prevent leakage on the face. The length of the nonorous portion should preferably be about 5% of the total length of the compression chamber.

A similar arrangement may also "be provided at the end remote from the inlet end of the com pression chamber, to prevent lubricant from exuding therefrom which might have undesirable consequences.

be extruded. Such materials as cemented car-..;-

bide hard metals produced by the technique of powder metallurgy are suitable, and in general it is preferred to use a hard metal consisting of" tungsten carbide, bonded with cobalt and processed to provide a capillary pore system with an average pore diameter of '7 microns, although the;

selected metal may vary according to the character of the material to be tableted and the pressure film of lubricant over the inslde wall of the porous metal die 5. If desired the pipe 22 or conduit 23 required for that purpose.

The porosity of the die should be suitably selected according to the nature of the material to be compressed and/or the viscosity of the lubricant to be used and the lubricant should be a viscosity suitable for enabling it to be discharged substantially uniformly over the porous inner wall of thedie, I

It has been found that Parafiinum Liquidum B. P. glyceryl triacetate or glycerin are suitable as lubricants in most cases, and that a die con-' structed so as to have a pore diameter of from 5-15 microns, with the majority of the pores smaller than 10 microns is suitable for use with these lubricants.

A preferred method of applying the invention to a known form of tableting machine is .illustrated by way of example in the accompanying drawing which is a part sectional elevation of the machine. It will however be obvious that the invention can equally Well be applied to other forms of tableting'machine.

Referring to the drawing:

The granulate to be tableted is contained in the hopper I, from which it is fed by gravity to the feed shoe 2, which is arranged to oscillate horizontally about a pivotal bearing 3 to and fro over the die plate 4, and at one end of its travel to allow a charge of granulate to enter the die 5. This die is constructed of porous metal, the end portions 21 however bein non-porous, and is so mounted within the die plate 4 as to be housed within or shrouded by non-porous metal. For this purpose it is preferred to mount the porous die 5 within a non-porous housing or sleeve 6 and to secure the thus assembled die within the die plate 4. The granulate is compressed within the die 5 between the top punch I and the bottom punch 8, the compressed tablet being expelled from the die by the bottom punch 8 at the top of its stroke.

The top punch 'l is mounted in a holder 9, having a pressure adjustment nut l0, whilst the bottom punch 8 is mounted in a holder l I, fitted with the punch. A similar up and down movement is imparted to the top punch I by means ofthe eccentric l9 mounted on the end of the shaft l5. Timed with these movements of the top and bottom punches, the cam It also produces a to and fro movement on the shaker rod 20, which in turn causes the feed shoe 2 to oscillate about its pivot 3, and to swing backwards and forwards over the 4 die plate, in a horizontal plane, covering the die aperture in each movement.

A reservoir of lubricant and a suitable source of pressure such for example as a pump, are diagrammatically illustrated at 2|, and are used to feed a supply of lubricant through the pipe 22 J and conduit 23 to the outer face of the porous metal die 5.

The conduit. 23 may conveniently feed the lubricant into a shallow annular spreader recess 24 provided in the inner face of the die housing 6, thus facilitating the spreading of the lubricant through a larger area of the porous metal and assisting in the maintenance of a may be divided into a plurality of branches, so

as to deliver lubricant to a plurality of parts of the die 5. One such branch is indicated at 25.

the lubricant continuously or intermittently, and if desired the pump strokes may be synchronised in any convenient way with the strokes of the punches. Means for controlling the flow of lubricant are shown at 26.

The operation of the machine will be readily understood from the following description of one tablet-compressing cycle of movements:

The bottom punch 8 having dropped to a predetermined point set by adjustment of the nut I3, the granulate flows from the feed shoe 2 into the porous metal die 5, the inner face of which is covered by a film of lubricant, which has exuded through its pores from the spreader recess 24. The feed shoe 2 swings back in the same horizontal plane, allowing the top punch I to come down, enter the die space and compress the granulate against the bottom punch 8, the die 5 acting as a former.

The rotary action of the eccentric l9 raises the top punch I out of the die and the cam [6 causes the pivoted member l8 to raise the bottom punch, the amount of lift being so adjusted by means of the nut l2, that at the top of the ejection stroke the face of the bottom punch is flush with the face of the die plate 4 with the tablet resting on the punch face. The timing is so arranged that there is a pause in the movementof the bottom punch 8 at thetop of its stroke, during which pause the feed shoe moves forward, and sweeps the tablet off the die plate into a container; the bottom punch then drops, the feed shoe continues its movement until its aperture registers with that of the die, when granulate again enters the die and the cycle is repeated. Meanwhile lubricant is supplied as described to the inner face of the die 5, thus greatly facilitating the easy discharge of the tablets.

The nature and porosity of the die 5 and the lubricant employed should of course be selected according to the material tobe tableted, but in general it is preferred that these should be selected according to the particulars stated above.

The following examples illustrate how a tableting machine constructed according to the invention can advantageously be employed:

Example 1 A granulation of dextrose monohydrate, which had been found by practice to require the addition of 2% of stearine to secure smooth ejection from the die, was effectively compressed and ejected without such an addition by means of this invention, using as a lubricant, Parafiinum Liquidum B. P. at the rate of 0.2 ml. per pump stroke, at avpressure of 60- lbs. per sq.,inch.

Example 2 A mixture of sodium acid phosphate and sodium citrate, required for use as a solution tablet, and normally requiring the addition of boric acid to secure smooth ejection was similarly produced, using either Paraffinum Liquidum B. P. or glyceryl triacetate as the lubricant.

Example 3 An acid-alkali mixture for the preparation of effervescent drink solutions, normally restricted in output because of the limitations of accepted procedure, was successfully tableted by means of this invention, using glyceryl triacetate as the lubricant at a rate of 0.4 ml. per stroke at a pressure of 80 lbs. per sq. inch.

Although the invention will find wide application in the tableting of drugs and chemicals for medical and like uses, it is not limited in this respect and may be found to be applicable to other purposes, such for example as the preforming of plastics.

I claim:

1. A tableting machine, comprising, a die of porous metal in which the material to be tableted.

is compressed said die being housed within a nonporous housing, and means for causing a liquid lubricant to be exuded through the pores of said porous metal so as to create a lubricating film over the face of the die.

2. A tableting machine, comprising, a die of porous metal in which the material to be tableted is compressed said die being housed within a non-porous housing, a reservoir for liquid lubricant, a conduit system connecting said reservoir with the interior of said housing and pressure means for feeding lubricant from said reservoir through said conduit system to the inner face of said housing and through the pores of said die.

3. A tableting machine as claimed in claim 1 in which the porous metal die is non-porous for a short portion of its length at the inlet end.

4. A tableting machine as claimed in claim 1 in which the porous metal die is non-porous for a short portion of its length at both its ends.

5. A tableting machine as claimed in claim 1 in which the housing provides a non-porous chamber extending therethrough containing the die member and the die member has a porous portion shorter than the depth of the non-porous chamber in which it is positioned and is so mounted in the housing as to leave a short nonporous portion at the inlet end of the chamber.

6. A tableting machine as claimed in claim 1 in which the housing provides a non-porous chamber extending therethrough containing the die member and the die member has a porous portion shorter than the depth of the non-porous chamber in which it is positioned and is so mounted in the housing as to leave a short nonporous portion at both ends of said chamber.

7. A tableting machine as claimed in claim 1 in which the porous metal die is constructed of hard metal carbide.

8. A tableting machine as claimed in claim 1 in which the porous metal die is constructed of tungsten carbide bonded with cobalt.

9. A tableting machine as claimed in claim 1 in which the pores of the porous metal die have diameters of from 5-15 microns, the majority of the pores being of a diameter smaller than 10 microns.

10. A tableting machine as claimed in claim 2 in which the porous metal die is constructed of tungsten carbide bonded with cobalt, the pores of said porous metal having diameters of from 5-.-15 microns, the majority of the pores being of a diameter smaller than 10 microns.

11. A tableting machine as claimed in claim 2 in which said conduit system is adapted to deliver lubricant at a plurality of parts of the innor face of the housing.

12. A tableting machine as claimed in claim 2 having a pump for feeding liquid lubricant from said reservoir to the inner face of said housing.

13. A tableting machine as claimed in claim 2 having means for continuously feeding lubricant from said reservoir to the inner face of said housing.

14. A tableting machine as claimed in claim 2 having means for intermittently feeding lubricant from said reservoir to the inner face of said housing.

CHARLES CREEVY.

REFERENCES CITED The following references are of record in the file of this patent;

UNITED STATES PATENTS Number Name Date 308,508 McFerran Nov. 25, 1884 1,289,570 Stokes Dec. 31, 1918 1,327,806 Bunde Jan. 13, 1920 2,043,085 Westin et a1 June 2, 1936 2,262,155 Andrews Nov. 11, 1941 

